As a kind of large volume underground vehicles, the subway greatly relieves the traffic pressure of the city. However, the main defect is a closed space can easily lead to high casualty once there is ...a fire. In this paper, Pathfinder software was utilized to simulate the evacuation in special subway station. The evacuation in dissimilar status was analyzed by setting up the fire scenario and changing the flow rate in the station. The results showed that the pressure of evacuation is mainly at stairway entrance and the width of exit has little effect on relieving the evacuation pressure. Besides, the number of the people in platform need to be restricted to 500 when the train is full; when the number of passengers in the train is 1542, that of people on the platform has to be limited to 480; when the number of passengers in the train is 1224, no more than 800 people on the platform need to be controlled.
As one of the most promising new energy sources, the lithium-ion battery (LIB) and its associated safety concerns have attracted great research interest. Herein, a comprehensive review on the thermal ...hazards of LIBs and the corresponding countermeasures is provided. In general, the thermal hazards of the LIB can be caused or aggravated by several factors including physical, electrical and thermal factors, manufacturing defect and even battery aging. Due to the activity and combustibility of traditional battery components, they usually possess a relatively high thermal hazard and a series of side reactions between electrodes and electrolytes may occur under abusive conditions, which would further lead to the thermal failure of LIBs. Besides, the thermal hazards generally manifest as the thermal runaway behaviors such as high-temperature, ejection, combustion, explosion and toxic gases for a single battery, and it can even evolve to thermal failure propagation within a battery pack. To decrease these hazards, some countermeasures are reviewed including the application of safety devices, fire-retardant additives, battery management systems, hazard warnings and firefighting should a hazard occur.
Electrolytes are involved in the thermal runaway (TR) process of cells, which is a potential hazard in lithium-ion batteries (LIBs). Therefore, the effects of different mass ratio of carbonate ...solvents (ethylene carbonate (EC)/propylene carbonate (PC)/ethyl methyl carbonate (EMC)) with LiBF4 and different environmental pressure on the combustion characteristics of electrolyte such as flame centerline temperature, mass loss rate (MLR) and heat release rate (HRR) were analyzed. The combustion process could be divided into four stages: ignition, stable combustion stage, stable combustion with flame color change stage and extinguishing; with the decrease of pressure, the MLR of electrolyte declined and the combustion time prolonged, while the temperature of flame centerline increased.
The electrolyte is one of the components that releases the most heat during the thermal runaway (TR) and combustion process of lithium-ion batteries (LIBs). Therefore, the thermal hazard of the ...electrolyte has a significant impact on the safety of LIBs. In this paper, the combustion characteristics of the electrolyte such as parameters of heat release rate (HRR), mass loss rate (MLR) and total heat release (THR) have been investigated and analyzed. In order to meet the current demand of plateau sections with low-pressure and low-oxygen areas on LIBs, an electrolyte with the most commonly used lithium salts, LiPF6, was chosen as the experimental sample. Due to the superior low-temperature performance, an electrolyte containing LiBF4 was also selected to be compared with the LiPF6 sample. Combustion experiments were conducted for electrolyte pool fire under various altitudes. According to the experimental results, both the average and peak values of MLR in the stable combustion stage of the electrolyte pool fire had positive exponential relations with the atmospheric pressure. At the relatively higher altitude, there was less THR, and the average and peak values of HRR decreased significantly, while the combustion duration increased remarkably when compared with that at the lower altitude. The average HRR of the electrolyte with LiBF4 was obviously lower than that of solution containing LiPF6 under low atmospheric pressure, which was slightly higher for LiBF4 electrolyte at standard atmospheric pressure. Because of the low molecular weight (MW) of LiBF4, the THR of the corresponding electrolyte was larger, so the addition of LiBF4 could not effectively improve the safety of the electrolyte. Moreover, the decrease of pressure tended to increase the production of harmful hydrogen fluoride (HF) gas.
Recently, with the extensive use of lithium-ion batteries (LIBs) in particular important areas such as energy storage devices, electric vehicles (EVs), and aerospace, the accompanying fire safety ...issues are also emerging and need to be taken into account seriously. Here, a series of experiments for LIB packs with five kinds of pack sizes (1 × 1, 1 × 2, 2 × 2, 2 × 3, 3 × 3) and three types of different state of charge (SOC) (100%, 50%, and 0%) were carried out using a cone calorimeter. Relevant fire parameters such as heat release rate (HRR), mass loss, and concentrations of CO, CO
2
, and O
2
were investigated. Remarkably similar combustion phenomena with intermittent jets were observed for LIB packs with 50% SOC and 100% SOC. The total mass loss (TML) and the peak value of HRR (pHRR) showed a similar positive correlation relationship of a power function with the surface area of the exposed heat source. For battery packs with 100% SOC, the pHRR of 3 × 3 cell module even increased by about 8 times to 12 kW. The content of toxic gas CO was evaluated by determining fractional effective dose (FED). It could be concluded that when the pack size was smaller than 2 × 3, the FED was below 1 for battery packs with 50% SOC and 100% SOC. This study can help predict the development patterns and fire risk of more large-scale battery fires and further diminish the thermal runaway (TR) hazard during an accident.
In this paper, the combustion characteristics of electrolyte containing carbonate and carboxylate solvents ethylene carbonate/dimethyl carbonate/ethyl methyl carbonate (EC/DMC/EMC) and EC/DMC/ethyl ...acetate (EC/DMC/EA) were studied by using the cone calorimeter. The results showed that when replacing EMC with EA, the flash point of EC/DMC/EA blend increased by 2.2 °C and the ignition temperature rose by 2.1 °C. When the external heat flux gained from 15 kW/m2 to 35 kW/m2, the difference between the peak heat release rate (pHRR) of the two samples widened from 57.3 kW to 111.1 kW, while the relative value did not change significantly, from 19.3% to 20.6%. In addition, the addition of EA increased the fire growth index (FGI) value of the electrolyte by 19.8% on average, which accelerated the fire development process. According to the results of flame temperature, after adding EA, the flame temperature decreased in the whole combustion process at 15 kW/m2, which reduced by 5.3% and 34.1%, respectively in the two steps. As the heat flux increased, the reduction amplitude declined. Thermochemistry (TC) theory was applied to verify the HRR values and change trend by calculating the theoretical heat release from normalized electrolyte molecules, and the results has been compared with those obtained from the cone calorimeter experiments based on the principle of oxygen consumption (OC) calorimetry, while HRR curves exported from the two methods were with the similar value and trend.
During the thermal runaway (TR) processing of lithium-ion batteries (LIBs), electrolyte would release most of the heat as the main component. Thus, study on the fire risk of electrolyte is conductive ...to quantitatively evaluate the safety of LIBs. In this work, the combustion characteristics of three kinds of carbonate mixture electrolytes and the composition of residue were investigated. The significant parameters from the cone calorimeter tests reflecting the thermal hazards such as heat release rate (HRR), mass loss rate (MLR) and open cup flash point were measured. The HRR curves at the radiant power of 15 and 25 kW/m2 were more gradual than those at 35 kW/m2 which had one or two apparent peaks. The addition of diethyl carbonate (DEC) increased the HRRs significantly. The applicability of thermal chemistry (TC) theory used to calculate HRR in previous works was studied. The results of TC technique had a disparity with those from the cone calorimeter called oxygen consumption (OC) calorimetry especially for the electrolyte containing DEC, which was proved by thermogravimetry-Fourier transform infrared spectroscopy (TG-FTIR) experimental results, while it is different from the conclusion reported in previous study. The constituent of carbonate electrolytes residue was analyzed by the X-ray Fluorescence (XRF). Element fluorine (F) accounted for over 90% of the residue. The open cup flash point and ignition temperature were determined by the open cup flash point apparatus. The results showed that the fire point was very close to the open cup flash point, and the difference was within 0.1 K.
The reason why heat release rate (HRR) of electrolyte blends containing diethyl carbonate (DEC) calculated by thermal chemistry (TC) theory existing errors when comparing with that from oxygen consumption (OC) calorimetry is that DEC promoted CO2 production through internal chemical reactions, while TC method regards all the CO2 production are from combustion during the heating processing. Thus, OC calorimetry is more appropriate than TC theory when calculating HRR of electrolyte mixtures containing DEC. The illustration is as presented in Figure GA. Figure GA. The mechanism of CO2 production influence on errors between TC theory and OC calorimetry. Display omitted
•The addition of DEC and EMC decreased the open cup flash points significantly.•The HRR curves of the three mixtures appeared extra higher peaks under higher radiation power.•The great disparity of CO2 production of the three samples leaded to the errors between TC theory and OC calorimetry.
As an important part in new energy storage devices, electrodes containing metals or their corresponding derivatives are widely used due to the diversity of material types, existing forms and assembly ...methods. In order to obtain novel energy storage components with superior performance, new technologies and studies on the improvement of electrode materials are emerging in recent years. This editorial paper aims to summarize the classical and latest research highlights on manufacturing, characterization and modification of metallic electrodes, especially new materials.
A workshop, as a crowded place, is quite easy to cause serious casualties and economic losses once there is a fire. In this paper, Pathfinder software was used to simulate fire emergency evacuation ...in a workshop of a large factory with building structural symmetry. According to the simulation results, several obstacles to the evacuation were discovered and further analyzed. The results showed that the main factors affecting the evacuation were the width of exits, the distribution of occupants and the effective evacuation width of stairs. Among them, only changing the width of exits had little influence on shortening evacuation time. While changing the effective evacuation width of stairs could greatly relieve the evacuation pressure, every increase of 0.5 m in the width of the staircase could shorten the evacuation time by 30.0 s. Meanwhile, the larger the number of people in high-rise buildings, the longer the evacuation time was. Therefore, the means of restricting people from entering the high-rise buildings in batches could be used to prevent personnel from being evacuated in time when a fire incident occurs.
Currently, the potential thermal runaway (TR) hazard of lithium-ion batteries (LIBs) has attracted widespread attention. Fortunately, water mist (WM) has proven to be an effective way to suppress TR ...in LIBs. This article mainly studies the TR characteristics and the WM suppression effects of three types of 18,650 cylinders with lithium iron phosphate (LFP), lithium cobalt oxide (LCO) and ternary nickel manganese cobalt (NMC) as the cathode materials. Based on the self-built platform, the TR suppression effect of pure WM and what with 5% NaCl additive by mass on three types of 18,650 cylinders at different state of charge (SOC) was explored. The results reveals that the WM containing NaCl additive possesses better inhibition effect of TR than pure WM; the WM has the best suppression effect on the LFP. However, WM cannot efficiently curb the TR of LCO and NMC at 100% SOC. Advancing the spraying time to the initial burst can effectively control TR of LCO and NMC at 66% and 33% SOC. The mechanism of WM to suppress TR is mainly reflected in cooling, diluting oxygen, affecting flames, and reacting with flue gas. In order to effectively inhibit the TR of LIBs, not only should a suitable TR inhibitor be selected, but also the timing of spraying should be considered. Only when both are the best choices, it is possible to control the TR hazard in the bud.
PDF
